At present, with the increasing transmission rate requirements, the baud rate of optical transmission systems continuously increases, which imposes increasingly higher rate requirements on components. To lower the rate requirements on components, multi-carrier modulation becomes a mainstream solution for optical communication systems. Currently, for multi-carrier modulation systems, a mode of independent and coherent reception of each carrier is commonly adopted in the industry. The independent and coherent reception of each carrier means that an independent set of coherent reception device should be equipped for each carrier, including a mixer, a PD (Photoconductive Detector, photoconductive detector), an ADC (Analog to Digital Converter, analog to digital converter), and a DSP (Digital Signal Processor, digital signal processor) processor.
A first piece of prior art provides a solution for coherent reception of a multi-carrier optical signal, where a multi-carrier optical signal (for example, a wavelength division multiplexed optical signal) is filtered through an optical filter to implement carrier separation, so as to obtain optical carrier signals; then each optical carrier signal is coherently mixed with its respective local optical signal corresponding to the center frequency of the optical carrier signal and is subjected to photoelectric conversion and analog-to-digital conversion, so as to obtain a digital baseband signal; and then digital signal processing is performed on the digital baseband signal, so as to recover an output signal.
A second piece of prior art provides another solution for coherent reception of a multi-carrier optical signal, where a multi-carrier optical signal is split through a power splitter, into multi-carrier optical signals whose number equals to the number of carriers; then each multi-carrier optical signal is coherently mixed with a local optical signal corresponding to the center frequency of its respective carrier, and is subjected to photoelectric conversion, so as to obtain an analog electrical signal containing information of the carriers, and the analog electrical signal is filtered to implement carrier separation, so as to obtain a carrier signal corresponding to the center frequency; and then, analog-to-digital conversion is performed on the carrier signal to obtain a digital baseband signal, and digital signal processing is performed on the digital baseband signal, so as to recover an output signal.
However, in the first piece of prior art, after the optical filter is used to filter the multi-carrier optical signal to implement carrier separation, an independent set of coherent reception device is required for each optical carrier signal while receiving the optical carrier signal. In the second piece of prior art, after the power splitter is used to split the multi-carrier signal into multiple multi-carrier signals, an independent set of coherent reception device is also required for each multi-carrier signal while receiving the multi-carrier signal, and different from the first piece of prior art, carrier separation is implemented by filtering the electrical signal. It can be seen from the above that, both the solution for receiving a multi-carrier optical signal in the first piece of prior art and the solution for receiving a multi-carrier optical signal in the second piece of prior art require multiple independent sets of coherent reception devices, and therefore, the solutions for receiving a multi-carrier optical signal in prior art have problems of high cost and high power consumption.